From U.S. Pat. No. 5,193,512, a tank-venting system is known which has: a tank with a tank-pressure sensor; an adsorption filter, which is connected to the tank via a tank-connecting line and has a venting line blockable by a shutoff valve; and, a tank-venting valve which is connected to the adsorption filter via a valve line. The tank-venting system assembled in this manner is checked as to operability according to the following method: a check is made as to whether an operating condition is present, for example full load, in which no significant underpressure can be built up in the tank after closing the shutoff valve and opening the tank-venting valve; if such a condition is present, the method is interrupted; otherwise, the following steps follow: closing the shutoff valve; opening the tank-venting valve; measuring the underpressure building up in the tank; and, determining the tank-venting system as not operational if a pregiven underpressure is not reached.
In the mentioned publication, a variant of the method is also disclosed according to which the shutoff valve and the tank-venting valve are closed and a check is made as to whether a pregiven overpressure builds up within a pregiven time span because of vaporizing fuel. If this is the case, the tank-venting valve is opened and a check is made whether a lambda control on the internal combustion engine has to carry out a lean correction. If this is the case, the tank-venting system is determined as being operational.
The arrangement described in the above-mentioned publication for checking the operability of a tank-venting apparatus includes units for performing the above-mentioned steps.
It has been shown that it is not possible to determine relatively small holes in the tank-venting apparatus with the method mentioned above. Accordingly, the problem existed to provide a method and an arrangement for checking the operability of a tank-venting apparatus on a motor vehicle having an internal combustion engine with which it is possible to also reliably determine relatively small holes.